The invention belongs to the technical field of combined walls and particularly relates to a combined wall which has the heat insulation function, the sound insulation function and the fireproof function. The combined wall is convenient to install and low in weight. According to the technical scheme, the fabricated environment-friendly external wall is provided with an external wall body, two hanging pieces, a heat insulating wall, a first keel, a filler wall, a second keel and an internal wall body, wherein each hanging piece comprises a cross rod and two installation plates which are vertically arranged on the same side of the cross rod, a cross groove is formed in each cross rod, the sizes of the two installation plates are the same, four installation holes are formed in each installation plate, the upper end and the lower end of the external wall body are inserted in the cross grooves of the two hanging pieces respectively, and the hanging pieces are connected to the heat insulating wall after multiple screws penetrate through the installation holes. According to the fabricated environment-friendly external wall, the requirements for heat insulation, fire protection, sound insulation and warming of an external wall are met in a one-off mode, industrialized manufacturing is achieved, construction is achieved on a site through one-time hoisting, working efficiency is greatly improved, and cost is reduced.